These American combat deaths — along with those of about 10 service members killed this year in Afghanistan and Iraq — underscore how a law passed shortly after the Sept. 11, 2001, terrorist attacks has been stretched to permit open-ended warfare against Islamist militant groups scattered across the Muslim world.

The law, commonly called the A.U.M.F., on its face provided congressional authorization to use military force only against nations, groups or individuals responsible for the attacks. But while the specific enemy lawmakers were thinking about in September 2001 was the original Al Qaeda and its Taliban host in Afghanistan, three presidents of both parties have since invoked the 9/11 war authority to justify battle against Islamist militants in many other places.

On Monday, Defense Secretary Jim Mattis and Secretary of State Rex W. Tillerson will testify before the Senate Foreign Relations Committee as lawmakers renew a debate over whether they should update and replace that law, revitalizing Congress’s constitutionally assigned role of making fundamental decisions about going to war.

But even as the Trump administration moves to ease some Obama-era constraints on counterterrorism operations, political obstacles to reaching a consensus on new parameters for a war authorization law look more daunting than ever. [Continue reading…]